C2 is of type char, and its size is only 1 byte. In other words, the maximum value can only be 256,322, and it overflows, so only the following values are obtained. Specific overflow methods can be found online. It's in the book, Tan Haoqiang's.

Then the value of c2 is 66. %d is output as an integer, that is, 66. Press %c to output, which is the value of ASCII code of c2, and is B.